package main

import "fmt"

func comma(s string) string {
	n := len(s)
	if n <= 3 {
		return s
	}
	return comma(s[:n-3]) + "," + s[n-3:]
}

func main() {
	fmt.Println(comma("hello World"))

	s := "abc"
	b := []byte(s)
	s2 := string(b)

}
